Strokes are currently the third leading cause of death in the United States, causing approximately 177,000 deaths per year, and strokes are currently the number one cause of long-term disability in the United States, currently affecting nearly 5 million people. Strokes are caused by an abrupt interruption of the blood supply to the brain or spinal cord, thereby depriving the tissue of oxygen and resulting in tissue damage.
Strokes typically occur in one of two forms: (i) hemorrhagic stokes, which occur with the rupture of a blood vessel; and (ii) ischemic strokes, which occur with the obstruction of a blood vessel.
Rapid diagnosis is a key component of stroke treatment. This is because the treatment for an ischemic stroke may be contra-indicated for the treatment for a hemorrhagic stroke and, furthermore, the effectiveness of a particular treatment may be time-sensitive. More particularly, the current preferred treatment for an acute ischemic stroke, i.e., the administration of tPA to eliminate blood clots, is contra-indicated for a hemorrhagic stroke. Furthermore, the clinical data suggests that the medication used to treat ischemic strokes (i.e., tPA) is most effective if it is administered within 3 hours of the onset of the stroke. However, current diagnosis times, i.e., the time needed to identify that the patient is suffering from a stroke and to identify the hemorrhagic or ischemic nature of the stroke, frequently exceeds this 3 hour window. As a result, only a fraction of current ischemic stroke victims are timely treated with tPA.
Imaging is generally necessary to properly diagnose (and hence properly treat) a stroke. More particularly, imaging is generally necessary to: (i) distinguish strokes from other medical conditions; (ii) distinguish between the different types of strokes (i.e., hemorrhagic or ischemic); and (iii) determine appropriate treatments (e.g., the administration of tPA in the case of an ischemic stroke).
Computerized Tomography (CT) has emerged as the key imaging modality in the diagnosis of strokes. CT imaging systems generally operate by directing X-rays into the body from a variety of positions, detecting the X-rays passing through the body, and then processing the detected X-rays so as to build a computer model of the patient's anatomy. This computer model can then be visualized so as to provide images of the patient's anatomy. It has been found that such CT scanning, including non-enhanced CT scanning, CT angiography scanning and CT perfusion scanning, is able to provide substantially all of the information needed to effectively diagnose (and hence properly treat) a stroke.
Unfortunately, in practice, the CT imaging system is typically located in the hospital's radiology department and the patient is typically received in the hospital's emergency room, and the “round-trip” time between the emergency room and the radiology department can frequently involve substantial delays, even in the best of hospitals. As a result, the time spent in transporting the patient from the emergency room to the radiology department and then back again can consume critical time which can compromise proper treatment of the patient (e.g., it can prevent ischemic stroke victims from being timely treated with tPA).
Thus, there is an urgent need for a new and improved CT imaging system which is particularly well suited for use in stroke applications. More particularly, there is an urgent need for a small, mobile CT imaging system which can be pre-positioned in the emergency room and moved to the patient so that the patient can be scanned at their current location, thus effectively eliminating “round-trip” delays and dramatically reducing the time needed to properly diagnose the patient. It is also important that the CT imaging system be relatively inexpensive, so as to facilitate its rapid proliferation and widespread use, e.g., pre-positioning in substantially all hospital emergency rooms and wide availability in outlying, low-volume settings (e.g., rural hospitals, ships, etc.).
In this respect it should also be appreciated that current CT imaging systems are generally quite large. This is due to (i) the general nature of CT imaging systems, and (ii) the anatomy that the current CT imaging systems are designed to scan.
More particularly, and looking now at FIGS. 1 and 2, current CT imaging systems generally comprise a housing A having a center opening B and enclosing a rotating drum assembly C, an X-ray tube assembly D adapted to emit X-rays, and an X-ray detector assembly E adapted to detect X-rays. X-ray tube assembly D and X-ray detector assembly E are mounted to rotating drum assembly C about center opening B, in diametrically-opposing relation, such that the X-ray beam F (generated by X-ray tube assembly D and detected by X-ray detector assembly E) is passed through the interior of the drum assembly C (i.e., across center opening B), and hence is passed through patient anatomy disposed within the interior of rotating drum assembly C (i.e., patient anatomy disposed within center opening B). Furthermore, since X-ray tube assembly D and X-ray detector assembly E are mounted on rotating drum assembly C so that they are rotated concentrically about the axis of rotating drum assembly C, X-ray beam F will be passed through the patient's anatomy along a full range of radial positions. As a result, by moving the patient longitudinally through center opening B while passing X-ray beam F through the anatomy along a range of radial positions, the CT imaging system can create the desired computer model of the scanned anatomy. Thus it will be appreciated that CT imaging systems must be large enough to fit, within the interior of drum assembly C, the patient anatomy which is to be scanned. Since conventional CT imaging systems are generally designed to scan any portion of the patient's anatomy, such CT imaging systems must have a center opening large enough to accept the torso of the patient B. Accordingly, conventional CT imaging systems are generally of substantial size.
Furthermore, since X-ray tube assembly D and X-ray detector assembly E are typically of substantial size and complexity (e.g., X-ray tube assembly D generally requires substantial power to penetrate the torso, and typically includes substantial power elements, cooling systems, etc., and X-ray detector assembly E typically includes substantial detector structure, etc.), and since X-ray tube assembly D and X-ray detector assembly E must remain fixed in position relative to one another with a high degree of precision even as drum assembly C is rotated at substantial speeds, X-ray tube assembly D and X-ray detector assembly E are typically mounted to rotating drum assembly C so that each assembly is concentric about the mid-point of the depth of the drum assembly. This arrangement minimizes cantilevering and provides the most stable mounting of X-ray tube assembly D and X-ray detector assembly E to rotating drum assembly C. Thus, with conventional CT imaging systems, X-ray beam F is positioned at the mid-point of the depth of the drum assembly. For purposes of the present invention, conventional CT imaging systems can be considered to have an “on-center” X-ray beam configuration.
The aforementioned construction of conventional CT imaging systems generally does not present a problem when the CT imaging system is a large, fixed-position installation designed to scan any portion of the patient's anatomy. However, such a construction presents a serious problem when trying to build a small, mobile CT imaging system intended to scan only the head of the patient, e.g., a potential stroke victim. This is because CT imaging systems having a center opening large enough to receive the torso of a patient must also have an overall size which makes it impractical to move the CT imaging system about the hospital.
Furthermore, it is not possible to solve the aforementioned problem by simply reducing the size of the CT imaging system so that it has a center opening just large enough to receive only the head of the patient. This is because the shoulders of the patient limit the extent to which the patient's head can be advanced into the center opening of the CT scanner. Thus, the conventional approach of locating the X-ray beam at the mid-point of the depth of the drum assembly (i.e., the aforementioned “on-center” configuration) prevents the lower portion of the head from being passed through the “on-center” X-ray beam. See FIG. 2A. This can be unacceptable for many potential stroke victims, who may be affected in the lower portion of the brain or the upper portion of the neck.
Thus, there is a need for a new and improved approach for positioning the X-ray tube assembly and the X-ray detector assembly within a CT imaging system, so as to facilitate the provision of a mobile (i.e., small) CT imaging system which can scan the entire head of a patient.